The liquid crystal display includes a display portion in which a plurality of pixels are arranged, is a display device that displays characters and images, and is widely used in devices such as mobile phones, laptop computers, and liquid crystal televisions. As such a liquid crystal display, the active matrix-driven liquid crystal display is widely known. This type of liquid crystal display includes an active matrix substrate (also referred to as an array substrate below), and the array substrate generally has wiring lines such as data bus lines and gate bus lines, pixel electrodes, and switching elements such as thin film transistors (TFT) in a region corresponding to the display portion (also referred to as a display region below).
In-plane switching (IPS) type liquid crystal displays include an array substrate in which a plurality of pixel electrodes and a plurality of common electrodes (opposite electrodes) are arranged at a gap from each other, and perform display by applying an electric field (horizontal electric field) to the liquid crystal layer, the electric field being substantially parallel to the surface of the substrate. The IPS method has an excellent viewing angle compared to general TN (twisted nematic) type devices. However, conventional IPS devices had a smaller light transmittance compared to general TN devices. This is because in conventional IPS devices, the pixel electrodes and the common electrodes mostly do not contribute to display.
As a method to mitigate this problem, the FFS method is proposed. FFS type liquid crystal displays perform display by applying a fringe field to a liquid crystal layer (an electric field including both horizontal and vertical electric field components). In FFS type liquid crystal displays, like in IPS devices, the pixel electrodes and the common electrodes are both formed on the array substrate, but the pixel electrodes and the common electrodes are disposed across an insulating layer from each other in the up-and-down direction. Normally, the electrodes disposed below (also referred to as lower electrodes below) are plate-shaped, and the electrodes disposed above (also referred to as upper electrodes below) have a plurality of slits formed therein to form an interdigital shape.
In the FFS method, the pixel electrodes may be either the lower electrodes or the upper electrodes. In the FFS method, the liquid crystal layer is driven by a fringe field generated between the upper electrodes and the lower electrodes. Thus, it is possible to drive the liquid crystal layer above the upper electrodes, and thus these portions can contribute to display. Thus, the light transmittance can be made greater than in conventional IPS devices.
As an FFS-type liquid crystal display, a liquid crystal display device that includes scan wiring lines, signal wiring lines, lower electrodes connected to the drain electrodes of the TFTs, and upper electrodes disposed above the lower electrodes across a protective film; second contact holes are formed in the protective film on a conductive pattern at the same potential as the lower electrodes in regions where the upper electrode is not formed and where light does not pass through, and a protective film is removed (see Patent Document 1, for example).